For a while I have been getting algae growth on my front wall, which establishes itself in a semi-cirle centered around the filter inlet. The rest of the front wall (Â±50%) is practically clear of algae.I tried to make pictures, but that turned out to be impossible, so . . . I concocted a mock-up to show the effect:The picture gives you the idea. However, the growth is quite severe, blocking out the view completely (within the semi-circle) after a few days.

I think what's happening here is the effect of accumulation of ammonia, produced by the fish, driven to the filter inlet by the flow of the water, thereby feeding the algae in that position. Once through the filter, the ammonia turns into nitrates, which doesn't seem to contribute to the algae growth.Besides, the nitrate level is very low (almost nil) as a result of the bog filter (picture shown in previous post:http://forums.tfhmagazine.com/viewtopic.php?f=142&t=28105)There are two tanks that show this effect. Both get direct morning sun, and both have bog filters.

What I am proposing to do is to increase the flow-through rate, hoping to capture the ammonia before it contributes to the algae growth.

Good idea! The problem is that the filter is internally fixed, and can't be moved, but I can position the intake of a canister filter in the other corner, and switch the internal filter off after I swap the media across.That should do it.

Well, that didn't take long at all!Approximately 36 hours after installing the canister filter and swapping the media around including cleaning the front wall of all algae growth, the algae grew again moving across to the new filter inlet on the other side of the tank.

So . . . if anyone can think of another likely solution, I'll stick with the ammonia explanation in the meantime. Another conclusion that I'm adopting is that it's ammonia that causes algae growth on the glass walls rather than nitrates. (I read somewhere that most algae prefer ammonia as a nitrogen source)

That was fast! So... the algae grows on glass nearest the 'old' aquarium water. That is, the water that has made a round of the tank and is now loaded with ammonia, CO2 and other wastes from the fish.

What happens if you turn the original filter back on, split the media between the filters, and run both? Can you get a good water flow pattern that results in half the water going into each filter? Maybe that would mean the wastes are more diluted, so the algae will not find it so rich near the 2 intakes compared to running just one filter.

Alternate:Build a manifold out of PVC and have several inlets spread across the back of the tank so that the 'old' water is not concentrated in one location until it is inside the pipes and out of the light. I have about 4-5 such inlets in tanks about 4' long, and 2-3 inlets in smaller tanks. I keep a sponge over the inlets.

Sorry Diane, I missed your post. Been away a few days.Anyway, I couldn't run the two filters at the same time. Didn't have enough media. However, I did buy some extra bags of it, but I can't run it on the Fluval. Must wait for the new filters.

[align=center]The Ammonia Vortex[/align]I think that I have found the mechanism of this effect by accident.I noticed the flow of the food flakes dropped on the water surface which gave me the idea.

What happens is that the filter output â€“ which is presumably devoid of any ammonia - is aimed along the back of the tank (see drawing):[align=center][/align]The flow turns at the side walls and then again along the front wall.It should be noted that the flow through the in and the outlet is equal, which means that the orbital flow is size restricted, picking up ammonia by mixing in the â€śoutskirtsâ€ť of the central ammonia cloud, indicated by the red area of the drawing.

The ammonia content is highest in the return leg of the current. Obviously, the algae on the front wall take full advantage of this, adopting an unfamiliar shape largely induced by the flow pattern.

The trouble is of course: How much ammonia is removed by the orbital current per unit of time?

Theory:The theory so far is that the water flow in the tank draws the Ammonia â€“ produced by the fish â€“ towards the filter inlet. This produces a â€śwandering algae patchâ€ť on the glass wall next to the inlet where the algae feeds on the Ammonia that â€śpasses byâ€ť.

Note: The term â€śAmmoniaâ€ť includes the ionised form â€śAmmoniumâ€ť.

Analysis:Ammonia production by the fish:Î”[amm]+ = p [mg/hr], where p = total Ammonia produced by the fish in mg, in one hour.Note: Î”[amm] indicates an incremental increase in the total amount of Ammonia.

Ammonia depletion by nitrification:The Ammonia enters the filter where it will be nitrified into NO3.Î”[amm]- = -F. [amm]/V [mg/hr], where F = effective output of the filter pump in litres of water per hour, V= the volume of the tank in Litres [L] and [amm] is the momentary total amount of Ammonia in the tank, in mg.

Note:â€śEffectiveâ€ť means that the output is 100% efficient in removing Ammonia from the tank. It will depend on the degree of mixing with the Ammonia in the tank.

Stability â€“ meaning that the Ammonia concentration remains constant - occurs when production equals depletion, hence:[align=center]F.[ amm]/V = p [mg/hr]or:[amm]/V = p/F [ppm] [/align] During a test intended to demonstrate the difference between planted and unplanted tanks (see: test-blog), it was reported that 130gram of fish (100 individuals), which were fed 3.0 grams of Tetra Prima per day, continuously produced 5ppm NO3 over 24 hours.This would equal an input of 1.45ppm of Ammonia in a 200L tank, which is 290mg total, or 12mg per hour.

But, there is currently less than 130gram of fish in that tank and the feeding rate is down to Â±2gram of Tetra Prima per day. On a linear relationship this would then equal 8mg of Ammonia per hour.The filter pump has a real output of Â±240L/hr (measured).It follows that: [amm]/V = 8/240 = 0.033 [ppm]

There are, of course, some questions about this number.

We cannot be certain that the bio filter is 100% efficient. Neither, whether P is equal to the real output. If not, then this would reduce the depletion rate and increase the final value.

0.033ppm is too low to measure with common test methods, but it is possible to concentrate the water sample, in this case at least 15 xâ€™s to achieve a number of Â±0.5ppm, which is the lowest reading on the set.

However, the number is a good indication of what to expect, besides, the conversion from grams of food per day into mg Ammonia per hour is very accurate. The only problem is the determination of P

Test:Iâ€™ve taken 1L of tank water from the center of the vortex, and decided to concentrate it 15 xâ€™s, meaning that 1L should be reduced to 67mL.To do that I poured the water into a clean stainless steel pan, which I then put on the stove to boil. Meanwhile, I installed an air blower aimed at the water surface to assist evaporation while the water was boiling (see picture):[align=center][/align]The entire operation took about 45 minutes, after which the sample was reduced to 68mL.Measurement Result: Â±0.4ppm, which â€“ taking the concentration into consideration â€“ translates to 0.03ppm .

This is remarkably close to the prediction of 0.033ppm. In fact both results are within 10% of each other.This means that: since the outcome follows the theory so closely and failing support to the contrary, then it is very likely that the theory is correct, meaning that low levels of Ammonia down to 0.03ppm supports the algae that covers the glass walls.Furthermore, it would appear that the effective output of the pump equals its real output @ 240L/hr, and that no further mixing of the Ammonia vortex and the orbital current is required.

A Â±1to1 flow (240L/hr in a 200L tank) still produces a material algae coating on the glass walls. ADA talks about people who have flows of 10x the volume of the tank per hr. IMO, that creates a lot of problems, and for what benefit?

I'm using about 2L of Siporax in my bio-filter, which appears enough at the moment, but If I ever want to increase the flow I may need to increase that volume.

Some further experimentation revealed something which I had not expected, although, thinking about it, I really should have.The point is that there is another significant ammonia depletion mechanism at work: the algae.I thought about it in the beginning, but decided that the algae would not be able to compete with the nitrification process, and so I ignored it, but . . .

To confirm my earlier conclusion that additional mixing would not have any effect, I installed a single pump aimed at the vortex in order to scatter it and thereby improve the mixing process.(see drawing:)[align=center][/align]I had a surprise when I tried to test the ammonia content the following day, finding it practically zero.I retried it a few more days in succession, but still: zero.By now the algae was extending over the entire front wall. This could mean only one thing: The algae were consuming the ammonia.There is obviously a lot more mixing taking place which makes the ammonia more distributed and therefore more available to the algae.Aside from the surprise, it provides additional proof that these algae consume ammonia.(Please note that, for the purpose of this post, â€śammoniaâ€ť includes the ionised form â€śammoniumâ€ť.)

Ammonia production by the fish:Î”[amm]+ = p [mg/hr], where p = total Ammonia produced by the fish in mg, in one hour.

Ammonia depletion:

by nitrification: Î”[amm]- = -F. [amm]/V [mg/hr], where F = effective output of the filter pump in litres of water per hour, V= the volume of the tank in Litres [L] and [amm] is the momentary total amount of Ammonia in the tank, in mg.

by algae consumption: Î”[amm]- = -Î± [mg/hr], where Î± = total Ammonia consumed by the algae in mg, in one hour.

The condition for stability remains the same, ie: production = depletion, so, it follows that:

[align=center]F. [amm]/V + Î± = p, and

[amm]/V = (p- Î±)/F [ppm][/align]

Since [amm]/V = 0, it follows that p = Î±, meaning that the algae are consuming all the produced ammonia.